Actually I doubt the cost of a spec ECU makes much of a difference to the cost of building a podium capable car.
What I do know is that there is every possibility of making a group B engine run well today - a local acquaintance has an original evo spec sport Quattro and it runs loud and clean. It's just so angry it's not even funny
Modern cars are just so very much faster, but I wish they sounded half as good...